1. Field of the Invention
The invention relates to a method for the manufacture of a gear part with a transversely directed profile, particularly a timing belt pulley, in which a substantially rotationally symmetrical workpiece is fixed in a flow-forming device and rotated and at least one profiled flow-forming tool is infed to a circumferential area of the workpiece and the transversely directed profile is shaped. The invention also relates to a gear part, particularly a timing belt pulley, which has a substantially rotationally symmetrical construction, a circumferential area and which is provided with a transversely directed profile.
2. Discussion of the Background
Methods and gear parts are e.g. known from DE 37 11 927 or DE 196 01 020. Thus, for example, toothed gears or timing belt pulleys are provided with transversely directed teeth forming a straight or helical tooth system in a circumferential area of a workpiece using a flow-forming machine through the radial infeeding of a profiled flow-forming roller. Such gear parts can be used in the most varied gears, which are inter alia employed in motor vehicle construction. Particularly in the latter field there is an ever greater need for gears, which are improved from the noise development standpoint.
The object of the invention is to provide a gear part with a good and in particular low-noise operating behavior and a method which is particularly suitable for the manufacture of the gear part.
The invention builds upon the aforementioned method in that prior to the shaping of the transversely directed profile the circumferential area of the workpiece is provided with at least one circumferentially directed groove and that the transversely directed profile is shaped axially on either side of the at least one groove.
A fundamental idea of the method according to the invention is consequently to provide the circumferential area of the workpiece with at least one circumferentially directed groove prior to the shaping of the transversely directed profile. Thus, in a simple manner it is possible to produce a transversely directed profile by flow-forming, because the circumferential groove permits an improved axial material flow. Following forming, the groove can be filled in an almost unchanged or complete manner.
According to a preferred further development of the method, the groove is constructed with a predetermined width in the outer circumferential area and the groove width is reduced during the forming of the transversely directed profile. Thus, in addition to the transversely directed profile, a particularly dimensionally stable, narrow groove can be produced.
The method according to the invention is in particular simplified in that during the forming of the profile material of the workpiece is displaced transversely in the direction of the groove.
As a function of the method steps utilized, different groove shapes can be produced. Thus, in a radially outer area the groove can be closed again, so that a circumferential channel is formed in the profile.
However, according to a preferred development of the method, the substantially rotationally symmetrical workpiece is produced by casting or forging. This makes it possible to utilize in each case specific advantages of cast and forged preforms, such as, for example, material characteristics or a special shaping. It is particularly advantageous if the at least one circumferentially directed groove is formed during casting or forging. An additional method step of introducing the groove in the workpiece can consequently be obviated.
Alternatively, the at least one circumferentially directed groove is introduced by radial infeeding of a forming roller in the circumferential area of the workpiece. This makes it possible to perform the method steps of introducing both the groove and the transversely directed profile on a flow-forming device. This permits a particularly rapid and therefore inexpensive manufacture of the gear parts according to the invention. In addition, on rolling in the groove, a notch effect in the material is counteracted. The groove depth preferably corresponds to the profile or tooth height or can be somewhat smaller or larger.
Fundamentally the groove could also be made in the workpiece in a metal-removing manner, such as by turning.
According to a further development of the method of the invention, it is advantageous that the substantially rotationally symmetrical workpiece is shaped from a circular blank in the flow-forming device. This also leads to the advantage that a further method step, namely the production of the rotationally symmetrical workpiece as a preform, can be carried out on the same flow-forming device. Thus, a complete machining of the gear part according to the invention can take place in a single setting.
A particularly simple manufacture of the circumferential area of the substantially rotationally symmetrical workpiece can take place by upsetting, splitting or wrapping round an edge of the workpiece (i.e. sloping the circumferential edge of the workpiece so that a rim is formed on the workpiece).
According to another preferred embodiment of the method, the at least one circumferentially directed groove is constructed as a circular channel. The substantially semicircular cross-section of the groove constructed as a circular channel reduces the appearance of stress peaks, so that a particularly material-protecting manufacture can take place.
Preferably the profile is formed in the circumferential area of the workpiece by means of a flow-forming roller or by means of a cross-rolling ledge or strip. Both possibilities permit a precise, rapid machining of the workpiece and are consequently particularly advantageous for an inexpensive manufacture of gear parts according to the invention.
In a further development of the method, a double helical tooth system is formed as the transversely directed profile and comprises two tooth system areas, which are arranged under a sweepback angle to one another. Thus, in the circumferential area of the workpiece it is possible to produce a double helical tooth system with a central groove and simultaneously a high quality of the double helical tooth system is maintained.
Preferably the two tooth system areas of the double helical tooth system are adjacent one another in a connecting area, which runs along the groove. Thus, in the case of high quality manufacturing both the tooth system and the intersection of the two tooth system areas can be produced in the sweepback angle.
The invention improves upon the aforementioned gear part in that the circumferential area has at least one substantially circumferentially directed groove and the transversely directed profile is arranged axially on either side of the groove. As a result of the at least one circumferential groove provided in addition to the transversely directed profile, it is possible to reduce vibrations occurring during the operation of the gear part, which ensures a good and particularly low-noise operating behavior.
This is based on the inventive determination that vibrations and noise during the operation of the gear part are inter alia caused by the compression of a surrounding medium, particularly air, between two meshing teeth. The additional groove, on either side of which is located the transversely directed profile, permits a better pressure compensation at the tooth and good air removal from the meshing tooth areas. This counteracts the formation of strong pressure pulsations and, as a result, the operating behavior is improved and the occurrence of vibrations and noise are reduced.
According to a preferred embodiment of the invention, the groove has a width which, in a radially outer circumferential area, is smaller than in a radially inner circumferential area. This has the advantage that the profile, on the one hand, has a particularly high mechanical stability and, on the other hand, the groove adequately strongly contributes to the reduction of vibration and noise, e.g. by absorbing and removing enclosed air. As a function of the axial extension of the transversely directed profile, it is also possible to form several circumferential grooves, which permits even better vibration reduction.
Fundamentally, as the transversely directed profile, use can be made of the most varied tooth shapes, which run in an inclined or right angle transversely to the circumferential direction. However, according to a particularly preferred embodiment of the invention, the transversely directed profile is constructed as a double helical tooth system. As a result of the teeth arranged in swept-back manner, flying off of the timing or toothed belt during operation is prevented, so that additional timing belt-guiding flanges on the two end faces of the toothed belt pulley are unnecessary. There is also a compensation of axial forces with this shape.
It is also preferable for the circumferential area to have a cylindrical construction, wherein in the central area a boss is provided and wherein the boss is connected to the circumferential area by means of a circular blank web. Such one-piece gear parts can be particularly inexpensively manufactured as a result of their material-saving, lightweight construction and can contribute to reducing the weight of machine or vehicle gears.
Finally, a preferred embodiment of the invention is characterized in that the circular blank web has an area, which is conical to the rotation axis. This makes it possible to choose the position of the tooth system of the inventive gear parts with respect to a driving shaft or a rotational axis as a function of specific requirements and to achieve a particularly rigid gear part.